Objective: To compare the amount of regulated upon activation, normal T cell expressed and secreted (RANTES) and monocyte chemotactic protein 1 (MCP-1) in follicular fluid (FF) of patients with and without endometriosis and to determine their oocyte fertilization and pregnancy rates. Design: Case-control study. Setting: Department of Obstetrics and Gynecology, University Hospital Schleswig-Holstein, Campus Luebeck, Germany. Patient(s): Thirty-two women with endometriosis stages I-IV and 28 women without endometriosis, both groups surgically and histologically confirmed. Intervention(s): Diagnostic laparoscopy, IVF-ET. Main Outcome Measure(s): RANTES and MCP-1 levels in follicular fluid, measured by ELISA, and oocyte fertilization and pregnancy rates. Result(s): Follicular response and days of gonadotropin stimulation were similar between the two groups. The levels of RANTES in FF from patients with endometriosis were significantly higher (460.4 ± 90.3 pg/mL) compared with concentrations in patients with tubal infertility (243.8 ± 70.9 pg/mL; P<.05). In contrast, MCP-1 concentrations in FF from women with endometriosis (330.0 ± 29.2 pg/mL) were lower than in women with tubal infertility (420.5 ± 46.6 pg/mL; P<.05). Oocyte fertilization rates in the endometriosis group (54%) were significantly lower than those of the tubal infertility group (73%; P<.05), as were the pregnancy rates (19% vs. 35%, respectively; P<.01). Conclusion(s): Women with endometriosis-associated infertility have a poor IVF outcome. Immune cell recruitment into the ovary might affect follicular function and lead to impaired oocyte quality.